Abstract
Owing to its modular construction, ability for bi-directional power flow and suitability for AC/DC grids, solid-state transformer (SST) is expected to be the backbone of the future smart grids. One of the main drawbacks of SST is the generation of negative-sequence current component at its input stage under unbalanced distribution system which causes adverse impacts on the power quality of the electricity grids. This paper is aimed at proposing a novel unbalance compensation method based on reduced order generalized integrator to suppress the negative-sequence current. Unlike the conventional sequence compensation method that is based on dual synchronous reference frames, the new proposed method does not involve complex calculation of the command current and sequence decomposition. As such, the response speed of the compensation controller is significantly improved. Additionally, the proposed method is easy to implement when compared with the current conventional compensation technique as there is no need to inject sequence components into the grid. A simulation model of three-module cascaded SST with three-phase star connection is established in Matlab/Simulink. Several case studies are carried out under different operating conditions. Simulation results validate the feasibility of the proposed method.
Highlights
Solid-state transformer (SST) is commonly regarded as a prototype of energy router, which is expected to have broad applications in the future smart power grids [1], [2]
Highvoltage power devices based on wide bandgap materials such as silicon carbide (SiC) IGBT that is capable of handling high voltage up to 25 kV are under development and soon they will be available for practical application [7]
IDEAL GRID AND BALANCED LOAD In order to verify the output power quality and operation stability of the SST with the proposed control scheme under ideal grid and balanced load, the grid voltage and load power for the three phases are assumed to be identical, i.e., 1:1:1
Summary
Solid-state transformer (SST) is commonly regarded as a prototype of energy router, which is expected to have broad applications in the future smart power grids [1], [2]. Unlike conventional power frequency magnetic transformer, SST is a combination of power electronic converters and medium- or high-frequency transformer, which can facilitate bi-directional power flow and is suitable for AC/DC grids [3]. Of an SST with a simple two-level or three-level converter into the distribution systems is not cost effective due to the high rated voltage of the required power devices [5]. As such, adopting cascaded stages or multilevel converters of cost-effective low-voltage power electronic devices has been investigated in the literature [6]. Highvoltage power devices based on wide bandgap materials such as silicon carbide (SiC) IGBT that is capable of handling high voltage up to 25 kV are under development and soon they will be available for practical application [7]. Combination of modular topologies and high-voltage power devices can acquire even higher voltage levels
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